The invention relates to a sealing device for a piston subjected to a pressure medium in a working cylinder, with a piston rod guide being arranged in or at the working cylinder and said rod guide comprising annular recesses and with elastic sealing rings as well as guide means being respectively disposed in the recesses according to Patent Application 199 26 450.3.
From the German Laid Open Patent Application DT 26 14 263 a dynamically adjustable sealing and guide device for pistons and piston rods is known which comprises at least two chamber rings arranged in series in the axial direction, and at least one sealing ring of an elastic material, which is located between them.
The piston has projections and recesses formed in the longitudinal direction, which are surrounded by a guide ring. A space is left between the guide rings for the accommodation of a sealing ring. The sealing ring rests against a groove in the piston via a further elastic ring, so that a certain adjustability is given due to the elasticity of the further ring.
The guide and sealing device for a piston subjected to a pressure medium in a working cylinder according to the German Patent DE 24 30 573 C3 is intended to prevent an axial displacement of the guide rings for an optimisation of the sealing effect and for reducing wear. For this purpose, the known positive fit of groove and collar with piston seals is utilised. Thereby, the disadvantageous deformation of the guide rings is to be prevented, on the other hand, however, the sealing effect between the rings and the piston is to be increased. The pressure build-up which is required at the spreader ring is to be enabled by openings in the piston.
According to the known teaching, a compression force is introduced through the openings to act on provided inclined surfaces. The provided elastic ring deflects the pressure in an upward direction so that all further rings can be biased towards a cylinder barrel (not shown).
Messrs Hunger DFE GmbH, Wxc3xcrzburg, also introduced a sealing system which can be biased externally. In this rod sealing system the sealing body has an integrated pressure duct via which the seal can be additionally biased by means of a contact pressure device. For this purpose the sealing body is penetrated by a hollow needle and additional pressure medium is supplied, adjustable to a fixed value, from the biasing device into the sealing body. This is to enable the balancing of the sliding or sealing behaviour, respectively, of the sealing elements in the installed hydraulic cylinder, with the lowest seal bias required for sealing being adjustable. The bias which is influenced by wear or fatigue after an extended service period can be changed, i.e. increased via the biasing device in order to increase the service life of the sealing system. As field of application for the presented sealing system which can be externally biased, hydraulic cylinders in machines and plants such as e.g. press cylinders, rolling mill cylinders, cylinders of civil engineering hydraulics equipment and so forth are known.
The cited solution, in particular, of the sealing system which can be externally biased by Messrs Hunger DFE GmbH requires a special sealing ring with the necessary pressure duct as well as an expensive clamping device with hollow needle and pressure accumulator. Thus, the known arrangement as a whole is expensive and cannotxe2x80x94or at least not economicallyxe2x80x94be employed as an emergency operation or quasi standby sealing device.
It was found that for example with so-called hydraulic upper piston die presses in the repair case, an upper hydraulic oil reservoir must be completely drained upon the exchange of one of the hydraulic cylinders or hydraulic pistons, respectively. Even after draining the hydraulic reservoir residual oil in a non-negligible quantity remains in the piston volume, which must be collected during the disassembly of the respective hydraulic cylinder, which makes the work considerably more difficult. For the above described case it would be desirable to provide the possibility of additional sealing in order to be able to exchange damaged primary seals which are located in the piston rod guide. Moreover, there should be the possibility to activate additional seals over a certain period of time, in order to ensure emergency operation properties of the relevant machines and equipment which employ hydraulic cylinders.
From the aforesaid it is therefore the object of the invention to specify an advanced sealing device for a piston subjected to a pressure medium in a working cylinder, with a piston rod guide known per se being provided in the or at the working cylinder and the rod guide comprising annular recesses, as well as elastic primary sealing rings as well as guide means being located in each recess, and with the device being provided with the possibility to ensure emergency operation properties in the emergency and/or repair case without having to rely on expensive special seals or extensive constructive modifications in the hydraulic cylinder system. In addition, it is to be ensured that the applied hydraulic pressure itself provides for the activation of an emergency seal.
The object of the invention is solved by means of a sealing device according to the characteristics as defined in claim 1, with claims 13 and 14 specifying special applications of such a device. The dependent claims comprise at least suitable embodiments and developments of the teaching described in the main claim.
The basic idea of the invention is to form at least one groove in the rod guide or in a cylinder ring downstream of the pressure chamber and concentrically surrounding the piston rod for the accommodation of a further quasi elastic emergency sealing ring, and to additionally provide means with the aid of which forces acting from the outside and radially to the piston rod can be applied to same, if required, so that the sealing ring is deformed similar to a crimp seal and brought into contact with the piston rod surface so that the desired sealing effect is ensured.
The elastic ring is to be a standard ring of the most simple construction, e.g. a so-called O ring, which is economically available. Due to the fact that only relatively low requirements with respect to long-term stability are to be met by the further sealing ring it is not necessary to employ expensive special materials.
In a first embodiment of the invention the additionally provided cylinder ring is located in a circumferential recess in the rod guide and more precisely at its upper end. The cylinder ring represents a supporting part which at least partially accommodates the elastic sealing ring, but, on the other hand, enables a lateral escape of the elastic sealing ring towards the piston rod in the case of the application of a force.
The supporting part can be adjusted in the axial direction of the piston rod, thereby driving the further elastic sealing ring and pressing same against an opposite stop face, so that the desired deformation of the sealing ring and the pressing or urging against the surface of the piston rod will result.
The mentioned stop face can be part of an mounting piece for accommodating one of the piston rod guide bands so that the additional constructive expenditure is kept within reasonable limits.
For the preferred application in a hydraulic upper piston die press, a plurality of sealable supply holes is provided in the rod guide, each of which enabling the actuation of a screw bolt by means of which the supporting part can be moved towards the cylinder frame.
In the case in which the guide rod must be disassembled for exchange purposes, e.g. of the primary seals, the supporting part is first moved via the screw bolt connection towards the stop face so that the further seal moves from a rest position into a sealing position towards to piston rod. This securely seals the working chamber of the hydraulic cylinder and the rod guide can be removed. Any hydraulic oil or similar fluid remaining in the working chamber need not be removed, collected and/or disposed of so that the repair times are shortened and the repair expenditure is reduced. There is, of course, also the possibility to activate the further seal in the operating case for ensuring the emergency operation properties, by effecting a corresponding adjustment of the supporting part so that a machine equipped with such hydraulic cylinders will still be available and thus usable for at least a certain time.
In a second embodiment the groove is formed as an annular duct in the rod guide, or in third embodiment it is formed in an annular supporting part above the rod guide and connected with same. Here, the groove represents an annular duct with a depth for the complete accommodation of the further sealing ring.
A medium supply duct extends in an essentially radially outward direction form the annular duct, with the former having a medium connection at its outer end in order to urge or move, respectively, the sealing ring located in the annular duct via a suitable fluid medium from its rest position into the sealing position and vice versa and against the surface of the piston rod. For the return movement, a vacuum may be applied to the medium connection.
The above mentioned medium supply duct can be routed through the cylinder frame, with the medium connection being formed at the cylinder frame in this case. The medium connection can be a standard plug or screw connection for the supply of pressurised fluid media.
With the second and third embodiment, in particular, there is the possibility to use an elastic sealing ring which comprises a biased steel spring ring which provides the sealing ring in the unloaded condition with the tendency to move in the upward direction, i.e. away from the sealing position. When the pressure application has overcome the bias of the steel spring ring, the sealing ring is moved from the rest position into the sealing position and deformed accordingly.
The cylinder ring mentioned with the embodiments or the annular supporting part surrounds the piston rod concentrically at a distance and is mounted at or in the working cylinder together with the rod guide.
An inventive configuration provides the possibility to form the further groove an a conical annular groove, with the width of the annular groove at the piston rod near end being smaller than the width of the piston rod far end. The conical annular groove is then communicating with a duct which opens into a space including a check valve. The spring loaded check valve closes a space opening to the outside. The space opening leads into a chamber or opens into such a chamber which can be filled with hydraulic fluid under operating pressure as the pressure medium, whereby the supply of the hydraulic fluid into the chamber can be blocked via e.g. a ball valve which can be screwed into a hole.
Due to the fact that the chamber with the valve in the open position is filled with hydraulic fluid via the supply duct, a pressure is built up against the check valve under overcoming the valve closing pressure. Thus, the hydraulic fluid flows to the piston rod far end of the conical annular groove. Due to the conical configuration of the groove, the force building up towards the piston rod is high enough with the given pressure conditions to achieve a contact pressure and sealing of the further elastic sealing ring against the surface of the piston rod.
With this embodiment, the operating hydraulic pressure is utilised in order to activate the emergency operating seal in the form of an O ring, with the shape of the annular groove providing for corresponding sufficiently high pressure forces of the ring.
As explained, the pressure device, i.e. the additional sealing ring, can be accommodated in a circumferential groove of the usual rod guide in order to enable an application as an additional emergency operation seal. Hereby, the sealing ring is activated through the application of pressure in the above described manner via a medium duct with corresponding medium connection and brought into the sealing position. Specific application cases here are cylinder arrangements of devices or equipment where a sudden leakage must be bridged for a certain time in emergency cases, such as e.g. landing gears of aircraft, water barrier constructions with hydraulic actuating means, positioning machines with hydraulic cylinders and so forth.
It is principally true that in the rest position a gap remains between the additional sealing ring and the piston rod. This gap ensures that e.g. in the case of a damage of the piston rod this damage does not result in an undesired surface change of the emergency operation sealing ring because there is no contact between sealing ring and piston rod. Upon a damage of the piston rod this can be repaired, e.g. by grinding the surface, with the sealing ring being brought from the standby position into the operating position where it ensures the desired emergency operation properties. In other words, under normal operating conditions there is no surface contact between the additional sealing ring and the piston rod so that there will be no wear of the sealing ring.